First I want to thank you all for your excellent suggestions. The A/C now works!
To make a long story short, it didn’t have enough refrigerant. The compressor clutch was not kicking in. Had the equilibrium pressure been near 90 psi I would have gone looking for a fault in the clutch control circuits. However with an equilibrium pressure of only 50 psi it was clear that the system was low on refrigerant. I figured that the low pressure switch might be open. If it was I could monitor it and just add refrigerant until the switch closed. However, I never figured out how to unplug the damned thing!
So I decided on adding refrigerant in 10 psi increments. After each 10 psi increase I would start the engine and see if the clutch would kick in and run the compressor.
The third 10 psi increment got the compressor cycling. Then, I followed the advice to turn on the A/C at it’s coldest setting and highest fan speed and then add refrigerant to the low side until the compressor stops cycling. That did the trick!
I turned the car off and let it cool for several hours. The outside temperature was 78 F The equilibrium pressure was now just over 90 psi. I started the car, turned on the A/C set to it’s coldest with the fan at it’s highest and inserted a thermistor probe into the passenger side middle outlet. The thermistor settled at a temperature of 48 F and the air blowing out was definitely chilly.
For the next few days I will check morning equilibrium pressures, and evenings, after the car’s been running, I will check for leaks with soapy water.
Thanks again for everybody’s help